Self-pollination is the process by which a rose's pollen fertilizes its own egg cells.
Among species roses, some have a mechanism that facilities self-pollination if cross-fertilization has not already occurred. Dr. Eileen W. Erlanson Macfarlane, a pioneer of genetic research in roses, described the process as follows:
"In many wild roses the petals are past their prime by the third day and the flowers no longer close at night. The stamens may then rise up and their delicate filaments curve over to bring the pollen-bearing anthers onto the receptive stigmatic heads of the ovaries. It was found...that the pollen cells mature before the embryo sac and egg cells. Most of the pollen is shed when the petals first open and insects will carry some...to flowers opening for the second day, which may then be ready for cross-fertilization. However, a few pollen grains remain on the shriveled anthers on the third day and the stigmas should still be receptive. The rising and incurving of the stamens could very well provide self-fertilization for any remaining eggs not already cross-fertilized. My experiments showed that the roses are self-fertile." Dr. Eileen W. Erlanson Macfarlane, "A Self-Pollination Mechanism And Other Items In Rose Species," in American Rose Annual, 1963, pp. 188-193.